Study on Pure IL VIV of A Free Spanning Pipeline Under General Boundary Conditions     

XU Wan-hai  XU Jing-yu  WU Ying-xiang  JI Chun-ning 《海洋工程》2017,31(1):114-122

Pipeline spans may occur due to natural seabed irregularities or local scour of bed sediment. The pure in-line (IL) vortex-induced vibrations (VIV) analysis of the free spans is an important subject for design of pipeline in uneven seabed. The main objective of this paper is to analyze the characteristics of pure IL VIV of a free spanning pipeline under general boundary conditions. An IL wake oscillator model which can describe the coupling of pipeline structure and fluctuating drag is introduced and employed. The coupled partial differential equations of structure and wake are transformed into a set of ordinary differential equations using two-mode Galerkin method. Some case studies are presented and thoroughly discussed in order to investigate the effects of internal fluid, axial force and boundary conditions on the pure IL VIV.  相似文献   

Contrasting hydrography and phytoplankton distribution in the upper layers of cyclonic eddies in the Mozambique Basin and Mozambique Channel     

T Lamont  RG Barlow 《African Journal of Marine Science》2017,39(3):293-306

Hydrographic data collected in cyclonic eddies in the Mozambique Channel and Basin revealed notable differences in temperature and salinity at a depth of 100 m, the upper mixed layer, the nitracline depths, and vertical distribution of chlorophyll-a (Chl-a). Differences in temperature and salinity did not show any consistent patterns. In contrast, the differences in the upper mixed layer, nitracline depths and the vertical Chl-a profile appeared to be driven by combined effects of eddy dynamics (i.e. shoaling of isopleths) and the seasonal variation in light availability and mixing conditions in the upper layers. Cyclonic eddies studied during austral spring and summer in the Mozambique Channel exhibited shallower upper mixed layers and nitracline depths, and deeper euphotic zones. Distinct subsurface Chl-a maxima (SCM) were associated with the stratified conditions in the upper layers of these eddies. In contrast, a cyclonic eddy studied during mid-austral winter in the Mozambique Basin had a shallower euphotic zone, deeper upper mixed layer and uniform Chl-a profiles. Another eddy sampled in the Mozambique Basin toward the end of winter showed a less pronounced SCM and roughly equal euphotic zone and upper mixed layer depths, suggestive of a transition from a well-mixed upper layer during winter to stratified conditions in summer.  相似文献   

基于HadCM3模式的我国主要气候区划界线时空预测研究     

杨强  郑西楠  何立恒 《干旱区地理》2017,40(1):17-25

气候区域分异规律及其时空演变研究是气候变化研究的核心内容之一。以1951-2014年中国气象数据和基于HadCM3模式的1950-2059年气象模拟数据为数据源来分析中国主要气候区划界线的时空变化趋势。结果表明：我国寒温带界线北移,且速度呈加快趋势;中温带和暖温带的北部界线向北移动,且东段界线的移动趋势较明显;亚热带北部界线已越过秦岭-淮河一线,且其东段北移趋势较明显;热带范围逐渐向北扩张。东北地区由湿润转干燥,达到干湿并存的状态;河西走廊、青藏高原和新疆地区总体上呈转湿趋势,虽北方半干旱区有部分区域转换为干旱区,但未出现明显的移动;华北平原等地区的湿润-半湿润界线和干湿区分界线均向西北方向移动;南方湿润区的干湿状况未发生显著变化。  相似文献   

鄂尔多斯盆地姬塬西部三叠系延长组长8油层组成岩作用与致密化过程^*          下载免费PDF全文

汪洋  刘洛夫  李树同  吉海涛  李林泽  罗泽华  许同 《古地理学报》2017,19(5):892-906

利用岩心、铸体薄片、扫描电镜、碳氧同位素及流体包裹体等资料,对鄂尔多斯盆地姬塬西部三叠系延长组长8油层组致密储集层特征进行了研究,重点分析了储集层成岩作用特征和储集层致密化成因机制及过程。研究区长8油层组砂岩主要为岩屑长石砂岩和长石岩屑砂岩,经历了压实—压溶、胶结、交代、溶蚀及构造破裂等成岩作用,整体处于中成岩A期晚期。典型成岩序列依次为机械压实、绿泥石黏土膜、早期(泥晶)方解石胶结、石英次生加大、长石、岩屑溶蚀、自生高岭石胶结、自生石英胶结、中期(含)铁方解石胶结。综合研究认为:(1)近物源伴随湖平面快速上升的沉积环境提供了储集层致密化的物质基础,不同沉积微相储集层物性差别较大,分流河道最好,分流间湾最差;(2)长8油层组原始孔隙度为41.35%,压实作用损孔率为50.67%,造成储集层孔隙度急剧降低,胶结作用损孔率为37.48%,导致孔隙度进一步减小,溶蚀作用仅增加了3.26%的孔隙度,难以有效改善储集层质量;(3)上述沉积与成岩因素共同导致储集层致密,致密化过程可分为压实孔隙骤减阶段、早期胶结减孔阶段、溶蚀作用增孔阶段和晚期胶结致密阶段共4个阶段;(4)油气大量充注期储集层孔隙度远低于10%,长8油层组先致密后成藏。  相似文献   

浅谈内蒙古大兴安岭地区中南部侏罗系与白垩系之界线     

曲洪祥  徐桓  龚全德  杜士澍  高文勃  仲米山  谭超  王一树  吴昊  张磊  陈泽翰 《地质与资源》2017,26(5):439-444

通过对大兴安岭地区侏罗系与白垩系之间不整合面的讨论,以地层区域对比及同位素测年数据等信息确定其界线,达到本区侏罗系与白垩系界线的可识别性、客观性和稳定性之目的.同时,对该区主要地层形成的大地构造环境的研究,认为土城子组是碰撞造山后伸展阶段形成的一套陆相红层,也是侏罗纪结束的标准层;而满克头鄂博组、玛尼吐组和白音高老组则是碰撞造山后垮塌阶段形成的火山地层.以大规模火山爆发为特征,本区开始了白垩纪地壳演化阶段.侏罗系与白垩系界线位于土城子组与满克头鄂博组之间,二者界线以区域不整合（假整合）为特征,不整合面形成于碰撞造山后伸展与垮塌的转换时期.  相似文献   

四川攀西红格矿区辉长岩和正长岩的SHRIMP U-Pb和Sm-Nd定年及其地质意义     

李华芹  王登红  张利国  任海涛  王晓地  贾小辉  杨文强 《地质通报》2017,36(5):698-705

用SHRIMP U-Pb和Sm-Nd定年技术,对攀西红格矿区含矿层状辉长岩、碱性正长岩进行了年龄测定。获得红格辉长岩中3种不同晶形锆石的U-Pb年龄分别为258.4±4.1Ma、1841±34Ma、2487±12Ma,由辉长岩、辉石和磷灰石所构成的Sm-Nd等时线年龄为253±14Ma;碱性正长岩中锆石的U-Pb年龄为257.2±1.5Ma。结果表明,红格辉长岩中具有典型基性岩锆石特征的锆石U-Pb年龄(258Ma)与同一地质样品的Sm-Nd年龄(全岩+矿物内部等时线年龄),以及同一矿区的正长岩锆石U-Pb年龄在测定误差范围内一致。鉴于层状辉长岩和碱性正长岩在空间上密切共生,在形成时间上一致,可以认为它们都属于晚二叠世末岩浆活动的产物;而1841Ma和2487Ma的锆石,可能是在基性-超基性岩浆的上侵过程中,从基底所捕获的岩浆锆石和继承锆石,其年龄信息,揭示了康滇地轴岩浆岩带的下部或结晶基底存在元古代甚至新太古代末期的岩石或物质。  相似文献   

维嘉海山沉积过程及其对西太平洋海山演化的意义          下载免费PDF全文

赵斌  吕文超  何高文  张宝金  韦振权  宁子杰  张旭东 《地球科学》2022,47(1):357-367

海山沉积过程与全球气候变化和古海洋演化有着紧密联系,维嘉海山保留了西太平洋晚中生代以来的完整沉积记录,是探索西太平洋海山构造演化的理想场所.基于浅地层剖面、大洋钻探和最新相关研究成果,通过研究海山的沉积特征、火山活动和沉降速率等,探索西太平洋维嘉海山晚中生代以来的沉积过程.结果显示维嘉海山顶部发育3个沉积单元,并发现了...  相似文献   

北京城区二氧化碳浓度和通量的梯度变化特征——I浓度与虚温          下载免费PDF全文

刘晓曼  程雪玲  胡非 《地球物理学报》2015,58(5):1502-1512

根据北京塔7层涡动系统2012年5月至2013年12月的湍流观测数据,分析了北京城区二氧化碳浓度在不同高度层次的日变化和月变化特征,并初步给出不同季节和日变化时间段内二氧化碳的浓度垂直廓线.结果表明:二氧化碳浓度整体随高度而下降;各观测层均有浓度的明显日变化,夏季最为明显,冬季相对平缓;近地层浓度直接受城市供暖、地表植被、交通运输等碳源影响,更高观测层浓度则受对流输送和天气过程影响较大;垂直方向上,冬季浓度变化范围最大,夏季层间浓度变化最明显;在一天中的任何时刻,近地面层二氧化碳浓度的日变化最低值一般出现在夏季,50m以上则出现在春季,浓度最高值总是出现在冬季;根据对二氧化碳浓度四季垂直廓线变化的分析可以看出,边界层二氧化碳浓度强烈受到碳源、下垫面植被、大气稳定度、环境温度和天气过程等因素的影响.  相似文献   

Prograded foredunes of Western Australia's macro‐tidal coast – implications for Holocene sea‐level change and high‐energy wave impacts          下载免费PDF全文

Max Engel  Simon Matthias May  Anja Scheffers  Peter Squire  Anna Pint  Dieter Kelletat  Helmut Brückner 《地球表面变化过程与地形》2015,40(6):726-740

The Holocene evolution of the Canning Coast of Western Australia has largely been overlooked so far mainly due to its remoteness and low population density. We report on new data from a sequence of foredunes inside the macro‐tidal Admiral Bay, 110 km southwest of Broome. Based on sediment cores, differential global positioning system (dGPS)‐based elevation transects, and stratigraphical analyses on outcrops of the relict foredunes, we aim at reconstructing Holocene coastal changes and relative sea levels (RSLs), as well as identifying and dating imprints of extreme‐wave events. Sedimentary analyses comprise the documentation of bedding structures, foraminiferal content and macrofaunal remains, grain size distribution, and organic matter. The chronological framework is based on 26 carbon‐14 accelerator mass spectrometry (¹⁴C‐AMS) datings. Marine flooding of the pre‐Holocene surface landward of the 2.5 km‐wide foredune barriers occurred 7400–7200 cal bp , when mangroves colonized the area. After only 200–400 years, a high‐energy inter‐tidal environment established and prevailed until c. 4000 cal bp , before turning into the present supralittoral mudflat. During that time, coastal regression led to beach progradation and the formation of aligned foredunes. Drivers of progradation were a stable RSL or gradual RSL fall after the mid‐Holocene and a positive sand budget. The foredunes overlie upper beach deposits located up to >2 m above the present upper beach level and provide evidence for a higher mid‐Holocene RSL. Discontinuous layers of coarse shells and sand are intercalated in the foredunes, indicating massive coastal flooding events. One such layer was traced over three dune ridges and dated to c. 1700–1550 cal bp . However, it seems that most tropical cyclones induce net erosion rather than deposition at aligned foredunes and thus, they are only suitable for reconstructing temporal variability if erosional features or sedimentation reliably tied to these events can be identified and dated accurately. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

移动荷载作用下土体动力反应数值模拟          下载免费PDF全文

张继强  冯瑞成  汤爱平 《地震工程学报》2015,37(3):778-781

在研究轨道振动荷载的产生机理基础上,归纳出一个能够涵盖速度、线路不平顺、轮重、轨枕对轮载的分散作用等因素在内的轨道荷载解析表达式,以此作为输入施加到土体模型上,利用ANSYS模拟地基土在轨道移动荷载作用下的三维瞬态弹塑性反应。通过计算得到土体不同位置位移和加速度时程曲线,并得出如下结论:荷载刚施加时地面位移会有一个突变,但是随着荷载的移动会达到一个稳定值,并随着水平面内远离轨道,该值逐渐衰减;荷载刚刚施加时加速度会有一个突变值,随着荷载的移动逐渐趋于零。轨道机车速度对竖向方向的位移和加速度影响不大。  相似文献